RFPRODUCTION OF HIGH DENSITY F₂⁺ CENTERS IN UNDOPED AND DOPED SODIUM FLUOWE CRYSTALS

F₂ centers in colored undoped and doped NaF crystals can be converted nearly completely into F₂⁺ centers with the high density of more than 10¹⁷cm^-3 by irradiating the crystals with a 505nm laser at room temperature. A process of conversion from F₂⁺ to (F₂⁺)* centers in the NaF crystals doped with divalent metal ions such as Mn⁺⁺, Mg⁺⁺ and Ni⁺⁺ after the 505nm laser irradiation was observed in our experiments.